This invention is an improvement on the inventions disclosed and claimed in Parkinson U.S. Pat. Nos. 3,839,256 and 3,908,066 entitled "Silicate-Resin Coating Composition" and "Protecting Metal and Metal Products", respectively. The Parkinson patents describe compositions, methods and coated electrical or magnetic grade steel for use in magnetic cores of transformers, motors and the like. The coatings described in the Parkinson patents have been used widely and successfully in commerce. However, there is still a problem evident from time to time with corrosion of the coated steel plate, particularly during storage and/or in use involving continuous viscissitudes of temperature and humidity. While a small amount of corrosion does not significantly affect the performance of the product in motors, generators and transformers, it hampers the salability of the product and generally raises questions of confidence by purchasers and users. When the surface is corroded, also, there is a tendency for the silicate-resin composition to separate from the plate.
The Parkinson patents disclose and claim the use of a class of quaternary ammonium silicates in combination with certain ethylene copolymers, terpolymers and comonomers, applied in an aqueous dispersion, to provide heat-resistant electrical insulation and lubricity. The complete specifications of U.S. Pat. Nos. 3,839,256 and 3,908,066 are incorporated herein by reference. The products they disclose have been successful in all respects including adhesion, toughness, lack of abrasiveness and relative thinness of coating; however, corrosion resistance has been difficult to impart to the substrate at the same time, along with the other desirable attributes.